1. Field
The present disclosure relates to a wireless communication system, and more particularly, to a method, an apparatus, software, or a recording medium that stores software, for transmitting or receiving a Channel State Information Reference Signal (CSI-RS) in a wireless communication system that supports Full Dimension Multi-Input Multi-Output (FD-MIMO) technology.
2. Discussion of the Background
The Multi-Input Multi-Output (MIMO) technology is to improve the efficiency of the transmission/reception of data using multiple transmission antennas and multiple reception antennas, as opposed to using a single transmission antenna and a single reception antenna. A receiving end may receive data through a single antenna path when a single antenna is used. When multiple antennas are used, the receiving end may receive data through multiple paths. Therefore, the data transmission speed and the amount of data transmitted may be improved, and coverage may be extended.
To increase the multiplex gain of an MIMO operation, an MIMO transmitting end may use Channel State Information (CSI) that is fed back from an MIMO receiving end. This may be referred to as a closed-loop (CL)-MIMO operation. The receiving end may determine a CSI by measuring a channel based on a predetermined reference signal (RS) obtained from the transmitting end. The CSI may include a rank indicator (RI), a precoding matrix index (PMI), channel quality information (CQI), and the like.
In the case where data is transmitted or received using multiple antennas, a channel state between each transmission antenna and each reception antenna is required to properly receive a signal. Therefore, a reference signal for each antenna port is needed. In the 3GPP LTE/LTE-A system, various reference signals are defined. For example, in the system according to 3GPP LTE release-8 and 9, Cell-Specific RS (CRS) that is transmitted for each subframe in a broadband, a UE-specific RS that is used for demodulating data, and the like, are defined. Also, in the system after 3GPP LTE-A release 10, a CSI-RS for measuring a channel, a DeModulation-RS (DM-RS) for demodulating data or Enhanced Physical Downlink Control Channel (EPDCCH), and the like, are additionally defined as new reference signals for supporting a maximum of 8 antenna ports in a downlink.
The existing MIMO wireless communication system has only supported 1-dimension antenna array (e.g., Uniform Linear Array (ULA) or Cross-Pole (or X-Pol)). The direction of a beam formed by the 1-dimension antenna array is specified by only an azimuth angle direction (e.g., a horizontal domain), and is not specified by an elevation angle direction (e.g., a vertical domain) and thus, only 2-dimension beamforming is supported.
Recently, for the purpose of improving the performance of the system, a wireless communication system that supports a 2-dimension antenna array has been developed. The wireless communication system is referred to as a Full Dimension MIMO (FD-MIMO) wireless communication system. However, a CSI-RS that supports the configuration of an antenna, which takes into consideration the FD-MIMO, has not yet defined.
Therefore, there is a desire for a method of designing a CSI-RS that supports the configuration of an antenna that takes into consideration the FD-MIMO.